Oh, honey. This is, in NO way, your fault. Suicide isn't something that's spontaneous. She had probably planned it out, and had her mind set by then. Even if she had had dinner with her son, I doubt that would have changed her mind.

You can't blame yourself. If you blame yourself, you'll just make yourself miserable hon. Your boyfriend needs you right now, and you couldn't be there for him if you yourself are so unstable. (Of course some amount is expected. Your boyfriend's mother just committed suicide. But you understand what I mean.)